Ask the Expert: When it comes to nitrogen tire inflation, how important is purity?

Q: When it comes to nitrogen tire inflation, how important is purity?

A:  Like winning in football: purity isn’t everything; it’s the only thing when it comes to nitrogen tire inflation. The higher the purity of the nitrogen in the tires, the greater the benefits. The goal is to achieve no less than 95 percent nitrogen purity IN the serviced tires or, more precisely, no more than 5 percent oxygen.

Tires that are properly inflated with nitrogen last longer, provide better fuel economy and enhance vehicle safety. Not all, but most of these benefits are a byproduct of the tires remaining at their proper pressure longer, which is a byproduct of nitrogen’s resistance to “permeation,” the natural process by which air seeps through a tire’s carcass, which in turn is the byproduct of nitrogen’s large molecular structure.

The air we breathe, and compress to inflated tires, is about 79 percent nitrogen and approximately 20 percent oxygen. Among other favorable properties, nitrogen has a very large molecular structure. A molecule of nitrogen is about four times the size of a molecule of the oxygen found in regular air. The concept is pretty simple: molecules of oxygen leak through a tire’s structure rather easily, at the rate of 1 to 3 psi per month. This is why tires always have to be topped-off: the oxygen in the air that is used to inflate tires leaks which, again, is entirely normal because oxygen has a very small molecular structure. Nitrogen molecules, on the other hand, are simply too large to leak through most tires. Now, consider that underinflated tires run warmer than properly inflated ones. This heat, combined with the change in how an underinflated tire contacts the road causes rapid, premature tire wear. Under inflation also increases “rolling resistance,” therefore requiring more energy to propel the vehicle riding on the underinflated tires. If you have ever ridden a bicycle or pushed a car with under inflated tires, you understand … it takes a lot more power. And, your vehicle is no different. Riding on underinflated tires is about the same as driving with your parking brake on.

So, the greatest benefits of nitrogen inflation have little to do with nitrogen itself and everything to do with removing oxygen; because, among other crimes, oxygen leaks out of tires very quickly. Hence, it follows that the higher the purity of the nitrogen in a tire the greater the benefits, mostly because there is simply less oxygen to leak out. 

To achieve a minimum in-tire nitrogen purity of 95 percent, using the industry standard “double purge” nitrogen inflation protocol, the nitrogen generator must provide a purity of about 98 percent. While some nitrogen generator manufacturers will dispute the necessity of a 95 percent minimum in-tire purity, citing Dalton’s Law of Partial Pressures and other “theories” that are irrelevant in the real world, their claims are not based upon the simple common sense facts of this requirement and are probably due to the inability of their nitrogen generation equipment to achieve these necessary high purities.  

Information provided by: Dan Brancaccio, National Sales Manager NitroFill, LLC